Module functions returning undefined in nodejs

Question

I am trying to return a value from module function and calling that function from different file, the function executes but return undefined
below is the code:

this is the module

teacherController={}
teacherController.getClassid = (req)=>{
    Teacher.findOne({token:req.session.user})
    .then((doc)=>{
        var classid = doc.class
        console.log(classid)   // this logs the correct value
        return doc;
    }).catch((err)=>{
        if(err) throw err;
    })
}
module.exports = teacherController;

this is where i am calling the module function

student.get('/ranking',(req,res)=>{
   var classid = teacher_con.getClassid(req);
   console.log(classid);  //this logs: undefined



});

thank you!

Pushprajsinh Chudasama · Accepted Answer · 2020-02-07 09:42:56Z

1

EDITED
You have to use the promise and thenable function.

 student.get('/ranking',(req,res)=>{
    teacher_con.getClassid(req).then(res =>{
        console.log(classid);  //you will get the doc
    });
 });

In module

    teacherController.getClassid = (req)=> { //use Promise
        return new Promise((resolve, reject)=>{
            Teacher.findOne({token:req.session.user})
            .exec((err, doc)=>{
                if(err){
                    reject(err);
                }
                else{
                    resolve(doc);
                }

            })
        });
    }

edited Feb 7, 2020 at 9:42

answered Feb 7, 2020 at 7:35

Pushprajsinh Chudasama

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4 Comments

Pushprajsinh Chudasama Over a year ago

Then you have to use promise , providing you snippet . @VirajPatil

Viraj Patil Over a year ago

vs code says "await has no effect on this expression"

Pushprajsinh Chudasama Over a year ago

Updated the code . @VirajPatil . It is working fine

Viraj Patil Over a year ago

Thank you so much @Pushprajsinh Chudasama ! Worked!!! Just edit console.log(classid) to console.log(res) in your answer :D thank you man

hoangdv · Accepted Answer · 2020-02-07 08:47:34Z

0

Return a promise in getClassid function:

teacherController = {}
teacherController.getClassid = (req) => {
  return Teacher.findOne({ token: req.session.user })
    .then((doc) => {
      var classid = doc.class
      console.log(classid)   // this logs the correct value
      return doc;
    }).catch((err) => {
      if (err) throw err;
    })
}
module.exports = teacherController;

Then, use async/await at your route:

student.get('/ranking', async (req, res) => {
    var classid = await teacher_con.getClassid(req);
    console.log(classid);
});

answered Feb 7, 2020 at 8:47

hoangdv

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1 Comment

Viraj Patil Over a year ago

i tried to return the promise but still got undefined ;_; <br>

teacherController.getClassid =  (req)=>{     Teacher.findOne({token:req.session.user}).lean()     .then( (doc)=>{         let promise = new Promise((reslove,reject)=>{             var classid = doc.class             reslove(classid);         })                  return promise;     }).catch((err)=>{         if(err) throw err;     }) }

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